The present invention relates to a dextrose in powder form with a high dextrose content, an essentially a crystalline form and a pronounced anhydrous nature, also having a rapid rate of dissolution in water, a particular particle size distribution and excellent flowability. The invention also relates to a dextrose in powder form of which the industrial use properties in direct compression are improved, and to a process for the preparation thereof.
Dextrose, produced industrially by hydrolysis of various starches, has been commonly used, mainly in the food industry, for numerous years.
Dextrose in powder form is used to advantage in pharmaceutical and food applications (notably in confectionery) where it is necessary to have dry products, for example, for the production of tablets or chocolate articles.
Three crystalline forms of dextrose are traditionally described, i.e. xcex1 dextrose monohydrate, anhydrous a dextrose and anhydrous xcex2 dextrose.
Although numerous processes have been proposed for directly converting glucose solutions to solid materials of any crystalline form, xcex1 dextrose monohydrate remains the virtually exclusive source of dextrose powder. This xcex1 dextrose monohydrate is traditionally produced by slow crystallisation, by cooling supersaturated syrups with a high glucose content originating from the hydrolysis of starch.
The main advantages thereof are its flowability and its low tendency to agglomerate, its chemical or physical stability during handling, its solubility in water, its whiteness and its sweet character without an abnormal taste.
However, its water content of about 9% in the form of water of crystallisation precludes its use in fields of application where problems relating to the moisture content of the finished products must be avoided.
Anhydrous crystalline xcex1 dextrose, a very pure crystalline dextrose with a low water content, was therefore chosen.
This anhydrous xcex1 dextrose is generally produced by dissolving the crystals of xcex1 dextrose monohydrate in water at temperatures from 60xc2x0 C. to 65xc2x0 C., for example, in autoclaves under a high vacuum and under carefully controlled operating conditions.
However, the anhydrous xcex1 dextrose thus obtained has the disadvantages of dissolving relatively slowly in water and having a tendency to cake during dissolution. In fact, a part of the anhydrous xcex1 dextrose is converted once again during this dissolution to xcex1 dextrose monohydrate which agglomerates and delays the dissolution of the anhydrous xcex1 dextrose accordingly.
In order to dissolve satisfactorily the two xcex1 monohydrate and xcex1 anhydrous forms, it is necessary, therefore, to use water at a high temperature or to add the dextrose gradually to water with stirring.
It has been proposed, therefore, to use anhydrous crystalline xcex2 dextrose which has a much better rate of dissolution compared with that of anhydrous xcex1 dextrose and even monohydrate.
However, it is well known to experts in the crystallisation of dextrose that although the transition point of the crystallisation of xcex1 dextrose monohydrate to anhydrous xcex1 dextrose is about 55xc2x0 C., that of anhydrous xcex1 dextrose to anhydrous xcex2 dextrose is about 110xc2x0 C.
Consequently, in order to obtain anhydrous xcex2 dextrose, it is necessary to operate at a high temperature at which dextrose is not very stable. This result limits all the more the industrial use of such a crystallisation process.
Moreover, as any dextrose in powder form composed of a single crystalline species and prepared in the traditional way is generally not very compressible, it is necessary to add maltodextrins or polysaccharides to it for the production of tablets.
However, the anhydrous products prepared in this way according to the prior art have generally been unsatisfactory because of problems of agglomeration and handling due to the maltodextrins or polysaccharides.
Patent application FR 2.398.802 describes a dextrose in powder form which has good flowability, does not agglomerate, is appreciably free from an unpleasant taste and coloured impurities but also has satisfactory compression properties.
The analysis of said dextrose in powder form reveals that it is composed of a mixture, in roughly equivalent amounts, of anhydrous xcex1 and xcex2 dextrose. The process for the preparation thereof by crystallisation and granulation is, however, particularly long and tedious.
Patent application WO 94/28.181 describes a dextrose which, apart from having a particularly low moisture content and a rapid rate of dissolution in water at ambient temperature, also has compression properties which allow it to be used for the production of tablets without the need for it to undergo special additional treatments or to add a binder.
However, the dextrose in powder form thus obtained is characterised not only by a composition containing the two anhydrous xcex1 and xcex2 crystalline forms with a high anhydrous xcex2 dextrose content of the order of 60 wt.% , but also by its amorphous nature, i.e. a degree of crystallinity only in the range 87% to 90%. Moreover, its dextrose content is only 94%, the remaining 6% being composed mainly of maltose and maltodextrins with a higher degree of polymerisation (DP).
It is apparent from the above that there is an unsatisfied need to obtain a dextrose in powder form with a high dextrose content and high crystalline purity and which also has excellent compression properties.
To its merit, the Applicant company has developed, after considerable research, a new dextrose in powder form.
The dextrose in powder form according to the invention is thus characterised initially in that it has:
a dextrose content at least equal to 99%,
an xcex1 crystalline form content at least equal to 95%,
a water content at most equal to 1%,
a compressibility, determined by a test A, at least equal to 80 N, preferably in the range 100 N to 200 N.
The dextrose content may be measured by a conventional high performance liquid chromatography method. It is determined here at a value at least equal to 99%.
The crystallinity is a measure of the crystalline structure or otherwise of the product. This crystallinity is determined according to measurements of the latent heat of fusion carried out using a differential calorimeter. The crystallinity of the product is determined by comparing the latent heat of fusion of the product with that of crystalline references having a variable proportion of xcex1 and xcex2 dextrose.
The degree of crystallinity for the anhydrous xcex1 form of dextrose in powder form according to the invention is determined at a value at least equal to 95%. The anhydrous xcex2 dextrose form is therefore in a small proportion, contrary to what may be found in commercial anhydrous products which nevertheless have similar compression properties.
The moisture content of the particles is also measured by traditional methods known, moreover, to the skilled person. The water content of said dextrose in powder form is thus at most equal to 1%, indicating a pronounced anhydrous character.
According to the invention the compressibility of the dextrose in powder form is determined by test A below, described in patent EP 220.103 owned by the Applicant company. This test A consists in measuring the force, expressed in newtons, which is representative of the compressibility of the dextrose in powder form studied. This force therefore reflects here the resistance to crushing of a tablet which is cylindrical with convex sides (radius of curvature 14 mm), having a diameter of 13 mm, a thickness of 6 mm and a weight of 0.764 g, i.e. an apparent density of 1.3 g/ml.
It is particularly surprising that a dextrose in powder form can simultaneously have a high dextrose content, at least equal to 99%, of which the anhydrous xcex1 crystalline form represents at least 95%, and a compressibility of at least 80 N, preferably in the range 100 N to 200 N.
In fact, it is conventionally accepted that the preparation of a dextrose in powder form having properties of high compressibility requires the mixing of xcex1 dextrose monohydrate with additives such as maltose and maltodextrins with a higher DP, or the production of mixed compositions of anhydrous xcex1 and xcex2 forms of dextrose, for example, by atomisation of a glucose syrup with a high dry matter content.
However, the dextrose in powder form according to the invention has a high compressibility, characteristic of said traditional dextrose in powder form, and a high crystalline purity of the anhydrous xcex1 form, characteristic of a crystalline dextrose with high purity and good chemical stability.
Consequently, and contrary to what was expected, it has a remarkably high compressibility for a crystalline purity never reached by the dextrose in powder form of the prior art.
By way of example, the dextrose in powder form sold under the brand names EMDEX(copyright), UNIDEX(copyright), ROYAL T(copyright) and CANTAB(copyright) in the field of direct compression are products in the monohydrate form. They are generally obtained by atomisation of a glucose syrup with a dextrose equivalent (DE) in the range 93% to 99%, as specified in appendix 3 of the monograph xe2x80x9cDextratesxe2x80x9d of the Handbook of Pharmaceutical Excipients.
A close analysis of their composition reveals, however, in the range 5% to 6% of maltose, maltotriose and maltodextrins with a higher DP.
With regard to the dextrose in powder form sold under the name xe2x80x9cDry Dextrose Anhydrous SD 99xe2x80x9d by CARGILL, which has excellent compression properties, in addition to its two anhydrous xcex1 and xcex2 crystalline forms and a little of contaminating xcex1 monohydrate form, it has an amorphous form content in the range 10% to 30%. Moreover, it does not generally comply with the monographs xe2x80x9cDextratesxe2x80x9d of the Handbook of Pharmaceutical Excipients.
The dextrose in powder form according to the invention is particularly suited to the production of tablets. In fact, according to the invention the anhydrous form characteristic of the dextrose in powder form has the advantage of avoiding the marked changes in hardness and texture associated with the migration of water itself due to changes in temperature, i.e. by successive periods of heating/cooling.
The dextrose in powder form according to the invention also has a high dextrose content and purity, which also gives the tablets prepared from said dextrose in powder form a better texture for the application of tablets to be chewed, avoiding the xe2x80x9cpastyxe2x80x9d nature of the tablets prepared from dextrose in powder form of the prior art.
The dextrose in powder form according to the invention may also be characterised by its rapid rate of dissolution in water.
In order to measure the rate of dissolution, 5 g exactly of the product to be tested are introduced into 150 ml of demineralised and degassed water kept at 20xc2x0 C. and undergoing agitation at 200 rpm.
The dissolution time corresponds to the time required, after the product has been introduced, to obtain perfect visual clarity of the suspension thus prepared.
Under these conditions, the dextrose in powder form according to the invention generally has a rate of dissolution of less than 10 s. Advantageously, it has a dissolution time of about 6 s.
These times are generally very much lower than those obtained with all the dextrose powders currently on sale.
The dextrose in powder form according to the invention may also be characterised by its apparent density and its friability.
The determination of apparent density is carried out using an instrument sold by HOSOKAWA under the brand name POWDER TESTER by applying the method recommended for measuring an apparent density.
Under these conditions, the dextrose in powder form according to the invention has a relatively low apparent density, generally in the range 0.5 g/ml to 0.7 g/ml, preferably in the range 0.55 g/ml to 0.65 g/ml.
The friability of said dextrose in powder form is determined according to a test described in the patent EP 645.096 owned by the Applicant company.
It has a value generally at least equal to 60, preferably in the range 60 to 80.
This low friability value is all the more remarkable in that the dextrose in powder form according to the invention has a low density. In fact, it is conventionally accepted that a dextrose in powder form is less friable the greater its density and compressibility.
Surprisingly and unexpectedly, and contrary to what is commonly accepted, the dextrose in powder form according to the invention does not conform with the rule according to which the lower the apparent density of a dextrose in powder form the more friable it is, that is, susceptible to a deterioration in its particle size by mechanical action.
The consequence of the combined improved properties of compressibility and friability is, in particular, to make the dextrose in powder form according to the invention particularly well suited to food and pharmaceutical applications.
The high compressibility of said dextrose in powder form allows, in fact, the production by simple direct compression of tablets with great hardness (for the application of tablets to be sucked) or of tablets of moderate hardness (for the application of tablets to be crunched).
Moreover, it is also possible to characterise the dextrose in powder form according to the invention by its mean diameter and its flowability, these properties being particularly suitable for said applications in compression.
The dextrose in powder form according to the invention thus generally has a mean diameter in the range 150 xcexcm to 200 xcexcm. These values are determined on a LASER LS particle size analyser with the brand name COULTER(copyright).
The flowability of the dextrose is evaluated using the POWDER TESTER instrument sold by HOSOKAWA. This instrument makes it possible to measure, under standardised and reproducible conditions, the flowability of a powder and to calculate a flow grade, also known as the Carr index. The dextrose in powder form according to the invention has an excellent flow grade, generally at least 70, preferably in the range 70 to 80. This value is generally equivalent to that of the dextrose powders of the prior art. This is particularly remarkable in that, compared with the prior products with the same flow, the dextrose in powder form according to the invention has a finer particle size.
Without wishing to be bound by any theory, it may be thought that the physical/chemical characteristics mentioned above of the dextrose in powder form according to the invention explain its excellent flowability. These characteristics relate in particular to its dextrose content, its crystalline purity, its centred particle size distribution but also the characteristic shape of its particles.
Dextrose in powder form may be obtained by carrying out a step involving the granulation of xcex1 dextrose powder having essentially the xcex1 crystalline form by the wet method using a binder, then an ageing step by drying the granular dextrose thus obtained. It should be pointed out that, as the Applicant company has observed, the product according to the invention cannot be prepared from a glucose solution by simple atomisation, crystallisation or granulation because in this case the remarkable compressibility properties can, in fact, be obtained only by the addition of additives, as pointed out above.
In order to obtain xcex1 dextrose in powder form according to the invention having the functional characteristics mentioned, the Applicant company observed that it was appropriate to choose, as the starting dextrose, a dextrose powder with a high dextrose content and having an essentially xcex1 crystalline form which can be obtained by crystallisation or atomisation.
The term xe2x80x9cessentially a crystalline formxe2x80x9d means a dextrose powder whose xcex1 crystalline form represents at least 95% of the crystalline forms which dextrose may take. The high dextrose content means here a value at least equal to 99%.
The particle size of said starting dextrose powder does not in itself constitute a limiting factor for producing a dextrose in powder form according to the invention.
The binder is composed of water or a glucose syrup with a dry matter content at least equal to 30%, preferably in the range 40% to 80%. As the proportion of dry matter provided by the binder gives at most 63% of the anhydrous xcex2 form and 37% of the anhydrous a form during the recrystallisation thereof, the glucose concentration of the binder is chosen such as to keep the level of the anhydrous xcex2 form of the final product at a value below 5%.
Surprisingly and unexpectedly, the Applicant company observed that the granulation of a dextrose powder by the wet method using a binder makes it possible to prepare, with a high yield, a product according to the invention in terms of its hygroscopic properties, its density, particle size distribution and flowability. In fact, the processes described earlier do not make it possible to obtain all the desired characteristics.
In order to carry out granulation, it is possible to use, for example, a continuous mixer-granulator of the vertical FLEXOMIX type sold by SCHUGI, or of the horizontal CB type sold by Lxc3x96DIGE into which the starting dextrose powder to be granulated is introduced continuously by way of a weight feeder, and the binder (water or a glucose syrup) is introduced continuously by way of a volumetric feeder.
Granulation may also be carried out in an atomisation tower or in a fluidised bed granulator. In a first preferred embodiment of the process for the preparation of a sorbitol in powder form according to the invention, a continuous mixer-granulator of the SCHUGI vertical FLEXOMIX type is chosen to be used. The starting dextrose powder and the binder are very intimately mixed in the mixer-granulator fitted with a shaft with knives arranged in the form of blades, and a system for spraying liquids by injection nozzles.
According to a preferred embodiment of the process according to the invention, good dispersion of the constituents and agglomeration of the particles of the starting dextrose powder are carried out by high speed agitation, i.e. at a value at least equal to 1500 rpm, preferably at least equal to 3000 rpm. At the outlet of the mixer-granulator, the granules formed are discharged continuously into a drier.
Discharge is carried out preferably by gravity in the case of said vertical granulator, and by pressure by way of the shaft of rotating knives if the horizontal granulator is used.
This second drying step at the outlet of the mixer-granulator makes it possible to remove the water originating from the binder and to crystallise the dry matter originating from the binder, if a glucose syrup was optionally used, such that crystallisation takes place after the prior granulation step.
Drying is carried out in two successive steps. The first step makes it possible to bring the water content of the moist granulated powder obtained at the outlet of the mixer-granulator to a value in the range 7% to 9% and the second drying step makes it possible to reduce the water content to a value at most equal to 1% so as to obtain the dextrose in powder form according to the invention.
The drier used in the first drying step may comprise, for example, a fluidised bed drier.
The drier used in the second drying step is a rotary drum or a vacuum oven as will be illustrated below.
The dextrose in powder form according to the invention is obtained after cooling and optionally sieving. In this case, the fine particles may be recycled directly to the start of granulation, and the coarse particles may be ground and recycled to the start of sieving or to the start of granulation.
In a second preferred embodiment of the process for the preparation of a sorbitol in powder form according to the invention, the choice is made to carry out granulation of the sorbitol powder by the wet method in an atomisation tower. In this case, the crystalline dextrose is introduced into said atomisation tower and water or a glucose syrup as defined above is introduced as binder.
The choice is made to feed an MSD (multi-stage dryer) atomisation tower with a water evaporation capacity of the order of 350 kg/h with dextrose powder at a flow rate in the range 400 kg/h to 600 kg/h, granulation taking place with water as binder, as will be illustrated below.
In view of the melting points of the various crystalline forms of sorbitol, the Applicant company found that it was necessary to monitor rigorously the operating temperatures of the atomisation tower.
It is advantageous, therefore, to adjust the temperature of the feed air to a value in the range 180xc2x0 C. to 200xc2x0 C., the vapour temperature to a value in the range 90xc2x0 C. to 95xc2x0 C. and the temperature of the static bed to a value in the range 70xc2x0 C. to 80xc2x0 C.
The dextrose in powder form according to the invention may be used advantageously, due to its functional properties mentioned above, as a sweetener or excipient in compositions used particularly in the food and pharmaceutical sectors. More particularly, said dextrose in powder form may be used advantageously in the confectionery sector, notably in chocolate making. Moreover, certain advantageous properties of said dextrose in powder form favour its use in applications of tablets to be sucked, chewed, dissolved, and swallowed.